Microstructure and microhardness of directionally solidified NiAl-W eutectic alloy

The microstructure and microhardness of directionally solidified NiAl-W eutectic alloys at growth rates of 2-25 mu m center dot s(-1)were investigated by a Bridgman crystal growing facility at a temperature gradient of 300 K center dot cm(-1). In view of the competitive growth between W dendritic and eutectic phases, W dendritic phase was eliminated, whereas the fully eutectic phase was prominent in the steady progress of the directionally solidified NiAl-W eutectic alloys. As the growth rate (V) increased, both the structure and solid/liquid interface of the directionally solidified NiAl-W eutectic alloys changed from planar to cellular. Both the fibrous spacing (d) and the diameter (a) decreased with increase in growth rate (V). The Vickers microhardness (H) of the directionally solidified NiAl-W eutectic alloys decreased with fibrous spacing (d) or diameter (a) increasing. The relationships ofHtodandawereH = 371.58d(-0.09)andH = 297.70a(-0.09), respectively.